Tielong Zhang On behalf of the CGS Team in the Institute of Geology and Geophysics, Chinese Academy of Science Spacecraft System and Payload China Geomagnetism Satellite Mission

Magsat  First high resolution vector field measurement  Nov 1979 – May 1980 – 7 month data Vector magnetometer and star tracker are not collocated Degraded vector data accuracy

 1991: Selection of idea to fly a magnetometer on a Danish satellite  : Feasibility study International Review, March 1992  1993: Funding for the total project decided Work package contracts Research Announcement  1995: First Ørsted International Science Team (ØIST) meeting 100 participants, 60 foreign  1997: Ready for launch!  1999: Launch on February 23 Ørsted Vector magnetometer co-located with star imager

Heritage  Ørsted Launched on 23 th February 1999 Polar orbit, km altitude all local times within 790 days (2.2 years)  CHAMP Launched on 15 th July 2000 low altitude (< km) all local times within 130 days  SAC-C Launched on 21 th November km altitude, fixed local time /22 30

China Mission Baseline  5 satellites constellation  4 polar orbit + 1 equtorial orbit  Identical payload for all satellites

Spacecraft System Architecture

Spacecraft Configuration  Main body plus tripod bracket  3 m deployable boom  Cross section ~0.4m 2

S/C Configuration

Spacecraft Configuration  Octagon Prism  Φ0.8m×1.0m

S/C Configuration  Main body Shape:  Octagon prism with a tripod bracket  On orbit status:  5m boom attaches to the bracket  Size:  Φ0.8m×3.5m (in Launch Status );  Φ0.8m×8.5m (in Flight Status) boom folded boom deployed

Main Technical Performance Specification

Mass （ kg ） Spacecraft95 Bus 25 ACS 6 OBDH 8 TC/TM 10 Thermal 6 Power 25 Boom 15 Payload10 System Contingency10 Total115 Spacecraft Mass Budget

Average （ W ） Maximum （ W ） Spacecraft40 AOCS 3 OBDH 15 TC/TM 1030 Thermal 5 Power supply 7 Payload20 Total6080 Spacecraft Power Budget

Structure and Mechanism Subsystem (SMS)  Structure:  The structure consists of several aluminum-honeycomb panels.  Mechanism:  Mainly mechanism:2 deployable Boom (for each is 2.5m long)  Function:  ensure a magnetic clean environment  stable accommodation for the sensors. Boom folded Boom deployed

Attitude and Orbit Control Subsystem (AOCS)  Attitude & Orbit Determination  ASC (star imager with 3 camera head) ×1  Magnetometer ×1  Sun Sensor ×1  GPS Receiver ×1  Attitude Control  Gravity gradient stabilization  3 Magnetorquers for active control ASC Magnetometer GPS receiver Attitude &Orbit determination Sun sensor Attitude control unit Magnetorquers On board CAN bus OBDH System AOC software Attitude Control

RF Communication Subsystem (RFCS)  The RFCS is responsible for  Telemetry, Tracking and Command (TT&C),  Payload data transmission.  The RFCS consists of communication receive & transmit device and two antennas.  Uplink and downlink in S-band  Downlink data rate is 2 Mbit/s;  Uplink date rate is 2 kbit/s.

Thermal Control Subsystem (TCS) Mode: passive means. Temperature range in cabin:-10°C － +35°C

On-board Data Handling Subsystem (OBDH)  The OBDH is responsible to:  data and task management;  onboard timing;  onboard command  The OBDH consists of :  on board computer,  tele-command unit,  payload data storage and control unit,  thermal control unit,  On board net: CAN bus.  On board computer:  20 MHz CPU  2 MByte SRAM

Power Supply Subsystem (PSS)  The PSS is responsible to:  Power generation,  Power distribution  Power storage.  Operation mode ：  the solar-panel generates electrical power in sunlight  Li-ion batteries supply power in eclipse.  PSS consists of solar panels, batteries and Power Control Unit  Solar panels ：  GaAs triple-junction  body-mounted solar panels  Area: ~3m 2  Output power: 150w in average;  Batteries ： 7-cell Li-ion battery packs, 10Ah;  Single-primary-bus mode distributes power to equipments (28.5±1V) 。

Orbital Parameter 。 EquatorialPolar Altitude550 km Inclination 15  87.4  ， 86.8 

Orbit  RAAN variation  15°equatorial ： period 49 day  87.4°polar ： period 1060 day  86.8°polar ： period 861day 15°equatorial 87.4°polar 86.8°polar

Orbit decay Equatorial Satellite

Orbit decay Polar Satellite 87.4

Orbit decay Polar Satellite 86.8

Orbit Decay EquatorialPolar 87.4Polar 86.8 Initial altitude km Altitude after 5 year km Time when altitude at 200km 9 yr 8 mth8 yr 4 mth

Eclipse  15°equatorial satellite ， longest eclipse duration 35.8min

Eclipse  87.4°polar satellite ， longest eclipse duration 36min

Eclipse  86.8°polar satellite ， longest eclipse duration 36min

Ground Stations for Data Receiving

 Equatorial satellite: Sanya station, 60 min visible time per day  Polar satellite, 3 stations, 80 min visible time per day for data downloading Ground station Orbits visible per day Visible time per day (min) Total visible time per day (min) 15°Sanya °Beijing Kashi Sanya °Beijing Kashi Sanya

Payload  Two fluxgate magnetometers  One scalar magnetometer  One star sensor